Hydraulically actuated rotating clutches and their associated control systems are being developed for both vehicle and marine engine driven power trains in order to better allow apportioned power delivery to the power train output shaft and to the engine driven auxiliary equipment, in accordance with the working conditions being experienced. Such selective division of power is preferably achieved through use of a closely controlled and continuously slippable disc-type clutch. This kind of clutch permits the delivery of a relatively low amount of power to the output shaft while at the same time allowing the engine to operate at a relatively high rate of speed. Subsequently, the vehicle or marine gear can be operated at a creeping rate of speed while also enabling auxiliary equipment, such as hydraulic pumps and the like, to be driven at an effectively high rate of speed.
The aforementioned diverse requirements have led to a wider introduction of disc-type slippable clutches and various centrifugally operated valves to better control them. For example, the rotating clutch and control system of U.S. Pat. No. 3,872,956 issued Mar. 25, 1975 to C. H. Herr et al, and assigned to the assignee of the present invention, incorporates a pair of rotating clutches which have been found particularly useful in a marine transmission for an ocean-going vessel. Each of the clutches incorporates a radially inwardly open actuating chamber with a rotating torus of fluid of selected depth therein for engaging the clutch actuating piston. Also operationally incorporated with each piston is a centrifugally operated valve which is exposed to the pressure of the fluid torus and is further responsive to a single source of fluid from the clutch control valve. While the system of the referenced patent is a considerable advancement in the art, it has been noted that when operating at a relatively low rate of rotational speed, the centrifugally responsive valve is less sensitive than desired to the relatively low pressure of the fluid torus. This has necessitated supplying fluid from the clutch control valve at a relatively low pressure and in a relatively narrow range of pressure of, for example, approximately zero to 35 psi. Consequently, the clutch control valve must be of more complex and sophisticated construction in order to obtain the desired response. Further, the centrifugally responsive valve of the referenced patent is subject to fluid flow forces through the valve that add to the difficulty of controlling it.
Further exemplifying the prior art efforts to produce continuously slippable friction clutches and centrifugally operated valves therefor, is U.S. Pat. No. 3,352,395 issued Nov. 14, 1967 to C. R. Hilpert. However, the centrifugally operated valves disclosed therein are relatively complex and costly in construction, such as requiring springs or compensating pins or the like, and are not sensitive to the pressure in the substantially closed clutch piston actuating chamber. Because these closed chambers are generally operated at relatively high pressures there is less need for their centrifugally operated valves to have a high degree of sensitivity.
It should also be noted that while a considerable number of prior art patents utilize a centrifugally responsive valve intermediate the control valve and a closed actuating chamber, they primarily serve to only quickly dump fluid from the chamber upon terminating operating pressure thereto. Alternately, they are specifically constructed to automatically release the clutch at either a predetermined low or predetermined high range of speed in order to protect the power train.